Resid cracking apparatus with catalyst and adsorbent regenerators and a process thereof

ABSTRACT

This invention provides a resid cracking apparatus comprising a riser, reactor, stripper cum separator with adjustable outlets in flow communication with adsorbent and catalyst regenerators for converting hydrocarbon residues containing higher concentration of conradson carbon content, poisonous metals such as nickel &amp; vanadium and basic nitrogen etc., into lighter and valuable products and a process thereof.

FIELD OF THE INVENTION

This invention relates to a resid cracking apparatus comprising a riser,reactor, stripper cum separator adsorbent and catalyst regenerator forconverting hydrocarbon residues containing higher concentration ofconradson carbon content, poisonous metals such as nickel & vanadium andbasic nitrogen etc., into lighter and valuable products and a processthereof.

BACKGROUND AND PRIOR ART OF THE INVENTION

Fluid Catalytic Cracking (FCC) is one of the key processes employed inpetroleum refineries for converting heavy vacuum gas oil into lighterproducts namely gasoline, diesel and liquefied petroleum gas (LPG).Processing of heavy residues e.g. atmospheric and vacuum bottoms areincreasingly being practiced in the FCC Unit for enhanced conversion ofresidue. Heavy residues contain higher amount of Conradson carbonresidue (CCR), poisonous metals e.g. sodium, nickel, vanadium and basicnitrogen compounds etc., all of which have significant impact on theperformance of FCC unit and the stability of its catalyst.

The high CCR of the feed tends to form coke on the catalyst surface,which in turn brings down the catalyst activity and its selectivity.Moreover, the higher deposit of coke on the catalyst increases theregenerator temperature and therefore catalyst/oil ratio reduces tomaintain the heat balance of FCC unit. The FCC catalyst can tolerate amaximum temperature of up to 750° C., which limits the CCR of feed thatcan be processed in FCC unit. At present, FCC unit with two stagesregenerators and catalyst coolers can handle feed CCR up to 8-wt %economically.

Nickel, vanadium and sodium are also present in large quantity in theresidual feed. The poisoning effects of these constituents are wellknown in the FCC art. In the past, there have been some efforts topassivate the damaging effects of nickel and vanadium on the catalyst.These efforts have resulted only with some success in the passivation ofnickel. Thus, by the known methods, it is presently possible to handleup to 30 PPM of nickel on the feed and up to 10,000-PPM nickel on theequilibrium catalyst. Similarly, with the known processes, vanadium upto only 30 PPM on feed and 15000 PPM on the equilibrium catalyst can behandled economically. These above limits pose serious problem of residueprocessing capability of FCC unit. As such, huge quantity of metal ladenequilibrium catalyst is withdrawn from resid FCC (RFCC) unit to keep thecirculating catalyst metal level within the tolerable limit. As regardsthe passivation of basic nitrogen compounds, suitable passivationtechnology is yet to be found.

In addition to the developments of passivation technologies, there havebeen some important design changes made in FCC for efficient residueprocessing. One such design change is the two-stage regeneration inplace of single stage regeneration. U.S. Pat. No. 4,064,038 teaches theadvantages of two-stage regenerator and its flexibility to handleadditional feed CCR without requiring catalyst cooler. However, evenwith two-stage regenerator of U.S. Pat. No. 4,064,038, there islimitation to increase feed CCR above 4.5-wt % and vanadium above 15–20PPM on feed.

It has been suggested in the art to use a separable mixture of catalystand demetallizing additive particles. For example, in U.S. Pat. Nos.4,895,637, 5,021,222 and 5,110,775, suggest a physically separablemixture of FCC catalyst and demetallizing additive having sufficientdifferences in their settling velocities so as to cover a segregation ofthe two types of particles in a single stage regenerator. Though such aprocess is simple, there are several practical disadvantages, whichlimit its resid-handling capability, namely (I) the regenerator is keptin the dense phase where the average superficial velocity is about 0.7meter/second. At such a velocity level, the catalyst particles stillpossess considerable downward gravitational pull. Moreover, there is asufficient turbulence and mixing in the bed, which leads to poorsegregation efficiency (II) it is known in the FCC art that vanadium ishighly mobile in the regenerator atmosphere, and that too in the singlestage regenerator, the vanadium may escape from the demetallizingadditive to the catalyst particle at these conditions. This defeats thebasic purpose of eliminating catalyst deactivation due to metalpoisoning.

Haddad et al has addressed some of these issues in U.S. Pat. No.4,875,994 where combustor type two-stage regenerator is proposed. Highvelocity combustion air is used to lift the catalyst particles from thecombustor. However, the mobile vanadium vapors are allowed to move tothe high temperature regenerator through lift line along with thecatalyst, which may cause considerable damage to zeolite in the catalystparticles. In addition, the downcomer line from the regenerator to thecombustor may allow the separated catalyst particle to again get mixedwith the additive. When very high CCR feed is processed, 1^(st) stageregenerator is expected to see high dense bed temperature. As theadditive cooler is provided at downstream of first stage regenerator, itis difficult to control dense bed temperature, which will furtheraggravate the destruction of zeolite structure.

U.S. Pat. No. 4,814,068 discloses a multistage process with three setsof intermediate riser, U bend, mixing and flue gas system. Such a schemeis used to separate large pore catalyst particles from those havingintermediate pores in regenerator. The purpose is to reduce hydrothermaldeactivation of ZSM-5 additive. The particle size of the coarseparticles is also very high (500–70000 microns) to avoid the carryoverof coarse particles to the second stage regenerator. The attritionresistance will be poor with such coarse particles.

Similarly, U.S. Pat. Nos. 4,990,314, 4,892,643 and 4,787,967 also coverseparation of two very different size particles one having 20–150 micronand the other 500–70,000 microns. Here the stripper section is madeannular double stage; thereby the difference in settling velocity of theabove two-size range of particles is exploited. The focus was tominimize the frequency of ZSM-5 additive regeneration. However, theseinventions do not address the issues related to minimization of metaldeactivation of catalyst and removal of feed CCR as arises in residueprocessing in FCC.

A process and apparatus is disclosed in U.S. Pat. No. 4,830,728 forupgrading naphtha in fluid catalytic cracking operation employingmultiple risers with a zeolite Y catalyst and ZSM-5 mixture. Separationof ZSM-5 having particle size in the range of 500–70000 microns fromzeolite Y catalyst of particle size range 20–150 microns in FCCstripper. A conical perforated plate or sieve provided at anintermediate location in stripper in such a way that larger & denserZSM-5 is retained above the plate/sieve and the smaller & lightercatalyst/passes through plate/sieve and settles at the bottom ofstripper. The separation mechanism adapted here is different from thepresent invention. Moreover, this patent does not address the issuespertaining to the problems of avoiding CCR and metal deactivation ofcatalyst while processing residue in FCC units.

The inventions of U.S. Pat. Nos. 5,059,302 and 5,196,172 claim of FCCprocess and apparatus employing a separable mixture of catalyst andsorbent particles. Here the adsorbent particles are smaller in size(30–90 microns) and the catalyst particles are bigger in size (80–150micron). The process employs selective vortex pocket classifier andhorizontal cyclone type burner/combustor to continuously separate thetwo types of particles and works based on the difference in centrifugalforces. As the segregation and regeneration of sorbent and catalyst iscarried out in first stage regenerator, the vanadium may migrate fromthe sorbent to the catalyst particle and destroy zeolite structure ofthe catalyst at such high temperature conditions.

U.S. Pat. No. 6,149,875 deals with removal of CCR and metal contaminantsin the heavy feed. However, the apparatus employed in this patent isdifferent from that of present invention. In addition, the differencebetween transport velocity of catalyst and adsorbent is exploited forsegregating catalyst from adsorbent. The superficial gas velocity inseparator vessel is very high and is operated in different domain(turbulent/fast fluidization) vis-à-vis bubbling bed regime of thepresent invention.

OBJECTS OF THE INVENTION

The main object of the present invention is to provide a resid crackingapparatus and process for converting heavy vacuum residue containinghigh concentration of Conradson carbon (CCR), metals such as vanadium,nickel and sodium into lighter products, by employing an adsorbent toremove one or more of the impurities from the feedstock before thefeedstock comes in contact with cracking catalyst.

Another object of the present invention is to provide an apparatuscomprising a stripper cum separator to separate catalyst from theadsorbent, before regeneration step for eliminating adverse effects ofvanadium (destruction of zeolite structure).

Yet another object of the present invention is to provide separatedoutlets for spent catalyst and adsorbent for regeneration.

Further object of the present invention is to provide a resid crackingapparatus with a stripper cum separator that handles the differences inthe particle size and density of catalyst and adsorbent particles.

Yet another object of the present invention is to provide longevity tothe catalyst, thereby increasing the production by lowering the cost.

Still, yet another object of the present invention is to provide acompatible design for said apparatus so that it can be used also withother FCC designs.

Another object of the present invention is to enhance the life of theapparatus by controlling the operating temperatures optionally by usingcatalyst coolers.

SUMMARY OF THE INVENTION

This invention provides for to a resid cracking apparatus comprising ariser, a reactor, a stripper cum separator, adsorbent/catalystregenerators in flow communication with the stripper cum separator withinterchangeable outlets depending upon the nature of catalyst andadsorbent, and a process thereof for converting hydrocarbon residuescontaining higher concentration of conradson carbon content, poisonousmetals such as nickel & vanadium and basic nitrogen etc., into lighterand valuable products and a process thereof.

DETAILED DESCRIPTION OF THE INVENTION

In order to achieve the above-cited objects, the present inventionprovides a fluidized bed catalytic cracking apparatus, said apparatus(FIG. 2) comprising:

-   -   a riser (35) containing a feed stock, regenerated catalyst and        adsorbent and having a first inlet means (31) for introduction        of high velocity steam, a second inlet means (61) for        introduction of the reactivated adsorbent, a third inlet means        (32) for introduction of the feed stock containing heavy        residual fractions with high concentrations of Conradson carbon        content, metals including vanadium and nickel and additional        poisons including nitrogen, a fourth inlet means (34) for        introduction of the regenerated catalyst, an outlet (35A) of the        riser is connected to riser termination devices/cyclones (39A,        39B, 40A and 40B) for causing separation of hydrocarbon vapors        from adsorbent-catalyst mixture, the cyclones having dip legs        extended towards stripper cum separator (37) drops        catalyst-adsorbent mixture close to the interface of catalyst        and adsorbent bed;    -   a reactor (38) comprising said cyclones and having an outlet        (41) for taking out hydrocarbon vapors and steam mixture to        fractionator(s);    -   a stripper cum separator (37) located at the bottom of the        reactor for causing removal of strippable hydrocarbons from        spent catalyst and coked adsorbent mixture and segregating        catalyst from adsorbent;    -   said stripper cum separator is with or without baffles/internals        having an inlet (36) at its base for introduction of steam in        the upward direction so as to provide a superficial velocity        sufficient to strip off all hydrocarbons and to segregate solids        into two layers i.e., layer of spent catalyst (62) and another        layer of coked adsorbent (63), an outlet at the bottom of the        stripper cum separator for taking out coked adsorbent through a        standpipe (52) via valve means (53), another outlet at an        intermediate location above the said adsorbent outlet (52) for        removing spent catalyst through a standpipe (42) via a valve        means (43);    -   an adsorbent regenerator (54) located below the level of the        lower portion of the stripper cum separator for receiving the        coked adsorbent from the bottom portion of the stripper cum        separator and causing reactivation of adsorbent thereof;    -   an inlet (59) in the adsorbent regenerator for introduction of        air or oxygen containing gas or steam, an outlet (60) in flow        communication with the third inlet (32) of the riser for        introduction of reactivated adsorbent; and another outlet (57)        at its top for the disposal of flue gas;    -   a catalyst regenerator (44) situated above the adsorbent        regenerator but below the stripper cum separator is connected to        the stripper cum separator by a stand pipe (42), an inlet (49)        at the base of the regenerator for introducing air or oxygen        containing gas for effectively burning coke deposited on the        catalyst, an outlet (50) in flow communication with the fourth        inlet of riser (34) via valve means (51) for introduction of        regenerated catalyst; and another outlet (47) at its top for        disposal of flue gas.

An embodiment of the present invention, wherein the outlets at thebottom and intermediate location of the stripper cum separator can belinked to the catalyst and the adsorbent regenerators respectively whenthe spent catalyst having particle size bigger and denser than that ofthe coked adsorbent.

Another embodiment of the present invention, wherein a fluidized bedcatalytic cracking apparatus, said apparatus (FIG. 3) comprising:

-   -   a riser (5) containing a feed stock, regenerated catalyst and        adsorbent and having a first inlet means (1) for introduction of        high velocity steam, a second inlet means (2) for introduction        of the reactivated adsorbent, a third inlet means (3) for        introduction of the feed stock containing heavy residual        fractions with high concentrations of Conradson carbon content,        metals including vanadium and nickel and additional poisons        including nitrogen, a fourth inlet means (4) for introduction of        the regenerated catalyst, an outlet (5A) of riser is connected        to riser termination devices/cyclones (9A, 9B, 10A, 10B) for        causing separation of hydrocarbon vapors from adsorbent-catalyst        mixture, cyclones having dip legs extended towards stripper cum        separator (7) drops catalyst-adsorbent mixture close to the        interface of catalyst and adsorbent bed;    -   a reactor (8) comprising said cyclones and having an outlet        means (11) for taking out hydrocarbon vapors and steam mixture        to fractionator(s);    -   a stripper cum separator (7) located at the bottom of the        reactor for causing removal of strippable hydrocarbons from        spent catalyst, and coked adsorbent mixture and segregating        catalyst from adsorbent;    -   said stripper cum separator is with or without        baffles/internals, an inlet means (6) at its base for        introduction of steam in the upward direction so as to provide a        superficial velocity sufficient to strip off all hydrocarbons        and to segregate solids into two layers i.e., layer of spent        catalyst (33) and another layer of coked adsorbent (32), an        outlet means (12) at the bottom of the stripper cum separator        for taking out spent catalyst through standpipe via valve means        (13), another outlet means (22) at an intermediate location for        removing coked adsorbent through stand pipe (22) via valve means        (23);    -   an adsorbent regenerator (24) located below the level of the        lower portion of the stripper cum separator for receiving the        coked adsorbent from the intermediate location of the stripper        cum separator and causing reactivation of the adsorbent thereof;    -   an inlet means (29) in the adsorbent regenerator for        introduction of air or oxygen containing gas or steam, an outlet        means (30) in flow communication with the second inlet means (2)        of the riser for introduction of reactivated adsorbent via stand        pipe (30), another outlet means (27) at its top for disposal of        flue gas;    -   a catalyst regenerator (14) situated above the adsorbent        regenerator is connected to stripper cum separator, an inlet        (19) at the base of the regenerator for introducing air or        oxygen containing gas for effectively burning coke deposited on        the catalyst, an outlet (20) in flow communication with the        fourth inlet (4) of riser for introduction of regenerated        catalyst via slide valve (21) and an outlet means (17) at its        top for disposal of flue gas.

Yet another embodiment of the present invention, wherein the particlesize of the spent catalyst is smaller than that of coked adsorbent.

Still another embodiment of the present invention, wherein the crackingcatalyst having a particle size in the range of 20–200 microns and aparticle density in the range of 1.0–1.8 g/cc.

Further embodiment of the present invention, wherein the adsorbenthaving a particle size in the range of 200–500 microns and a particledensity in the range of 1.5–3.0 g/cc.

Still another embodiment of the present invention, wherein the catalystregenerator having two stage cyclones means (55 and 66) for separationof flue gas from adsorbent particles.

Yet another embodiment of the present invention, wherein the adsorbentregenerator having adsorbent cooler means (58) for removal of excessheat from adsorbent regenerator bed.

Still another embodiment of the present invention, wherein the catalystregenerator having two stage cyclones means (45 and 46) for separationof flue gas from catalyst particles.

Yet another embodiment of the present invention, wherein a portion ofthe coked adsorbent is directly routed to the riser from stripper cumseparator outlet (52) via stand pipes (60A) without undergoingreactivation step.

Still another embodiment of the present invention, wherein the particlesize of the spent catalyst is bigger than that of the coked adsorbent.

Yet another embodiment of the present invention, wherein the crackingcatalyst having a particle size in the range of 200–500 microns and aparticle density in the range of 1.5–3.0 g/cc.

Further embodiment of the present invention, wherein the adsorbenthaving a particle size in the range of 20–200 microns and a particledensity in the range of 1.0–1.8 g/cc. Still another embodiment of thepresent invention, wherein a portion of the coked adsorbent is directlyrouted to the riser from stripper cum separator outlet (22) via standpipes (30A) without undergoing reactivation step.

Yet another embodiment of the present invention, wherein stripping ofentrained hydrocarbons from spent catalyst-coked adsorbent mixture andsegregation of spent catalyst from coked adsorbent take placesimultaneously in the stripper cum separator.

Further embodiment of the present invention, wherein the rising bubblesare the driving forces for particle segregation in the stripper cumseparator.

Still another embodiment of the present invention, wherein thesuperficial gas velocity in stripper cum separator is in the range of0.05–0.4 m/s, preferably in the range of 0.10–0.20 m/s for particlesegregation.

Yet another embodiment of the present invention, wherein superficialvelocity of the gas in the stripper cum separator varies within therange of ±20% of minimum fluidization velocity of larger and denserparticles for ensuring fluidization and segregation.

Still another embodiment of the present invention, wherein thesuperficial velocity in the adsorbent regenerator is in the range of0.5–2.0 m/s, preferably in the range of 0.8–1.5 m/s.

Yet another embodiment of the present invention, wherein 100%segregation of catalyst from adsorbent is achieved even within theprevailing operating conditions of conventional fluid catalytic crackingstrippers.

Further embodiment of the present invention, wherein the difference inminimum fluidization velocity of smaller and lighter particles and thoseof larger and denser particles is used to achieve the desiredsegregation.

Still another embodiment of the present invention, wherein cokedadsorbent that is separated from spent catalyst in stripper cumseparator, is in reducing environment thereby eliminating adverseeffects including the destruction of Zeolite structure of vanadium onthe catalyst.

Further embodiment of the present invention, wherein the riser extendsthrough stripper cum separator following the separation of hydrocarbongas from catalyst-adsorbent mixture or an external riser.

Yet another embodiment of the present invention, wherein the mass flowrate of the adsorbent to the riser is such that the heat carried by theadsorbent is sufficient to vaporize heavy hydrocarbon feed stock andmass flow of adsorbent is in the range of 20–60wt % of total solidscirculation.

Further embodiment of the present invention, wherein said adsorbentcomprises micro spheres selected from a group consisting of calcinedclay, calcined and crushed coke, magnesium oxide, silicia-alumina and abottom cracking additive for selective removal of metals and feed CCR.

Yet another embodiment of the present invention, wherein said catalystcomprises catalysts selected from the group consisting of Rare earthexchanged Y zeolite, ultra stable Y zeolite, non-crystalline acidicmatrix and other zeolites selected from type ZSM-5.

Still another embodiment of the present invention, wherein partial andcontrolled burning is performed in said adsorbent regenerator to preventtemperature excursions beyond 690° C. to enhance the life of theadsorbent.

Yet another embodiment of the present invention, wherein diplegs ofriser termination devices/reactor cyclones are located at the interfaceof spent catalyst and coked adsorbent mixture in stripper cum separator.

Further embodiment of the present invention, wherein stripping ofentrained hydrocarbons from spent catalyst-coked adsorbent mixture andsegregation of spent catalyst from coked adsorbent simultaneously takeplace in stripper cum separator.

Yet another embodiment of the present invention, wherein said strippercum separator is with or without baffles/internals.

Still another embodiment of the present invention, wherein the valvemeans provided on the stand pipes are slide valves.

The present invention also provides a Fluidized catalytic crackingprocess for converting hydrocarbon residues containing higherconcentrations of Conradson carbon content, metals including nickel,vanadium, sodium and basic nitrogen into lighter products, wherein theparticle size of the catalyst is smaller and lighter than the adsorbent,said process comprising the steps of;

-   -   a) contacting heavy residue feed stock with hot adsorbent, said        adsorbent is lifted with steam from the riser bottom for such        contact, to make the heavy residue feed, free from all        contaminants;    -   b) contacting the feed depleted of contaminants with the        catalyst at an intermediate location of the riser to cause        catalytic cracking reaction;    -   c) transporting the vapor products, the spent catalyst and the        coked adsorbent mixture to the riser top pneumatically;    -   d) separating the catalyst and the adsorbent from product        hydrocarbon vapors in the riser termination device;    -   e) separating the spent catalyst and coked adsorbent in a        stripper cum separator located below the reactor, at a low        temperature, as two distinct layers of spent catalyst and coked        adsorbent depending upon the particle size, density and        differences in their minimum fluidization velocity, by using        steam, so that heavier particles of coked adsorbent are settled        at the bottom of the stripper cum separator and the lighter        particles of spent catalyst are settled at the intermediate        location of the stripper cum separator and all the strippable        interstitial hydrocarbons are stripped off from the cracking        catalyst and adsorbent mixture in said stripper cum separator;    -   f) introducing the coked adsorbent into adsorbent regenerator        for partial or complete removal of coke by using air or oxygen        containing gas for reactivation;    -   g) transporting the reactivated adsorbent into the riser;    -   h) transporting portion or full of coked adsorbent into the        riser without reactivation;    -   i) introducing the spent catalyst into catalyst regenerator for        partial or complete regeneration of catalyst using air, oxygen        or oxygen containing gases; and    -   j) transporting the regenerated catalyst into the riser;

Step (e) of the above-mentioned process is also be performed byseparating the spent catalyst and coked adsorbent in a stripper cumseparator located below the reactor, at a low temperature, as twodistinct layers of spent catalyst and coked adsorbent depending upon theparticle size, density and differences in their minimum fluidizationvelocity, by using steam, so that heavier particles of spent catalystare settled at the bottom of the stripper cum separator and the lighterparticles of coked adsorbent are settled at the intermediate location ofthe stripper cum separator and all the strippable interstitialhydrocarbons are stripped off from the cracking catalyst and adsorbentmixture in said stripper cum separator;

Yet another embodiment of the present invention, a process wherein thesuperficial velocity of steam in stripper cum separator is maintained inthe range of 0.05–0.4 and preferably in the range of 0.10–0.20 m/s forefficient stripping and particle segregation. Still another embodimentof the present invention, a process wherein the superficial velocity inthe adsorbent regenerator & catalyst regenerator is maintained within0.5–2.0 m/s and preferably within 0.8–1.5 m/s.

Yet another embodiment of the present invention, a process wherein saidadsorbent is calcined coke for heavy feed stock containing ConradsonCarbon content (CCR) in the range of 8 wt %-20 wt %

Still another embodiment of the present invention, a process wherein theseparation of spent catalyst and coked adsorbent is done in stripper cumseparator in the absence of Oxygen, at a low temperature in the range of450–600° C., thereby preventing Vanadium mobility from adsorbent tocatalyst.

Yet another embodiment of the present invention, a process wherein thepreferred adsorbent for residue feed containing a very high CCR above 8wt % is calcined petroleum coke having good attrition resistance.

Still another embodiment of the present invention, a process whereinwithdrawing net coke stream from the adsorbent regenerator especiallywhile processing residual oils containing CCR above 8-wt %.

Yet another embodiment of the present invention, a process wherein a netstream of coked adsorbent is withdrawn from the system to maintain heatbalance easily with high Conradson Coke content up to 20-wt %.

Further embodiment of the present invention, a process wherein the airis maintained to achieve total combustion in catalyst regenerator andthe coke on regenerated catalyst is preferably less than 0.1 wt %,resulting in control of regenerator temperature within the range of730–750° C.

Still another embodiment of the present invention, a process whereincoked adsorbent from the stripper can be recycled directly withoutundergoing reactivation.

Yet another embodiment of the present invention, a process wherein theresidue feed stock comprising a very high CCR to the extent of 20 wt %of feed is processed without violating the overall heat balance of theunit and not resorting to catalyst cooling.

Yet another embodiment of the present invention, a process whereinConradson coke and metal laden adsorbent can be withdrawn as separatestream from the stripper cum separator or from adsorbent cum catalystregenerators, such adsorbent containing metals as high as 35,000 ppm forthe extraction of high value Vanadium and nickel from the adsorbent.

Further embodiment of the present invention, a process wherein theadsorbent is selected from the group consisting of magnesia, silicamagnesia, kaolin clay, alumina silica alumina and a mixture thereofhaving acidic and non-acidic properties.

Yet another embodiment of the present invention, wherein said processhandles up to 40 PPM of nickel on feed.

Still another embodiment of the present invention, wherein said processhandles up to 15000 PPM of nickel on equilibrium catalyst.

Further embodiment of the present invention, wherein said processhandles vanadium on feed up to 60 PPM.

Yet another embodiment of the present invention, wherein said processhandles vanadium up to 20000 PPM on equilibrium catalyst.

Still another embodiment of the present invention, a process wherein thetotal residence time from the adsorbent entry point to catalyst entrypoint in the riser bottom section is in the range of 10–40% of the totalriser residence time.

Yet another embodiment of the present invention, a process wherein thecatalyst residence time in the riser is maintained between 1–15 secondsand preferably between 3–8 seconds depending on the severity of theoperation.

The present invention is further described in the form of the followingpreferred embodiments.

Adsorbent

Adsorbent particles are intended to adsorb the CCR, the poisonous metalse.g. vanadium, nickel etc., basic nitrogen and sulfur rich compoundsexisting in enriched form in the residual hydrocarbon fractions.Typically, adsorbent particles are having particle size in the range of200–500 microns but preferably within 300–400 microns. The particledensity is between 1.5–3.0 g/cc and preferably 1.8–2.6 g/cc and mostpreferably 2.3–2.5 g/cc. The present system also supports when theparticle size of adsorbent smaller than the particle size of thecatalyst.

The adsorbent particles mainly consist of the microspheres composed ofalumina, silica, magnesia, silica alumina, silica magnesia, kaolin clayor a mixture there off having acidic properties or totally non-acidic.These micro spheres are prepared using the conventional art of FCCcatalyst preparation i.e., by preparing the solution of desired chemicalcomposition, its spray drying and calcination. Typically, thesematerials have very less acidic cracking activity characterized by MATactivity of less than 15 and surface area less than 5 m²/g. However, thepresent invention is not limited to low activity adsorbent alone. Forexample, one may use the disposable spent catalyst from FCC/Residue FCCor hydro-processing units, provided the particle size and density arewithin the specified range of the adsorbent as mentioned above. Moredetails on the above said materials are available in U.S. Pat. Nos.5,059,302 and 6,148,975.

For residues containing CCR above 8 wt %, it is preferred that theadsorbent should be calcined petroleum coke produced from calcination ofraw coke generated in the delayed coking process of petroleum residues.Coal particles or other types of coke are also applicable but calcinedcoke is preferred due to its excellent attrition resistance and physicalproperties.

Typical properties of calcined petroleum coke is given below:

Description % wt Ash content 0.17 Sulfur 1.04 Volatile matters 0.33 Iron149 ppm Vanadium 3.8 ppm Real density 2.14 g/cc Bulk density 0.73 g/ccParticle density 1.52 g/cc Attrition resistance 1.2 Division Index

Typical particle size distribution of the adsorbent particles are givenbelow:

Wt % below Adsorbent Particle Size (microns)  0 210 10 230 30 250 50 27070 290 90 310 95 320 100  350

More details on adsorbent are discussed in U.S. Pat. Nos. 4,944,865 &6,149,875. The adsorbent particles preferably should be micro sphericalin nature. However, the present invention is not limited to microspherical form only.

Catalyst

Conventional state of the art commercial catalyst used in resid FCCtechnology is also employed in this invention. However, the presentinvention specifically describes the particle size of the catalyst to bewithin 20–200 microns and more preferably 20–170 microns and mostpreferably 20–120 microns. Similarly, the particle density may be within1.0–1.8 g/cc and more preferably 1.3–1.6 g/cc and most preferably within1.3–1.5 g/cc to obtain best results as disclosed in the presentinvention. Like adsorbents, catalyst should be preferablymicro-spherical in shape. The present invention is not restricted tospherical type of FCC catalyst particles. Rare earth exchanged Yzeolite, Ultrastable Y zeolite, non-crystalline acidic matrix and evenother zeolites e.g. shape selective ZSM-5 zeolite may also be used. Thepresent system also supports when the particle size of the catalyst isbigger than that of the particle size of the adsorbent.

Typical particle size distribution of the catalyst micro spheres is:

Wt % below Catalyst Particle Size, Microns  0 20 10 40 30 70 50 80 70 9590 105  95 110  100  120 Feedstock

The present invention provides a novel approach to handle residualhydrocarbons having higher CCR, metals and other poisons. Maximumbenefit is obtained particularly if the metal level and CCR level of thefeed are above 10 ppm and 5 wt % on feed respectively. Here, metalincludes vanadium and nickel. It may be noted that our inventionpreferentially allow the CCR, metals and other poisons of the feed todeposit on the adsorbent first before contacting with the catalyst.Moreover, a net stream of coked adsorbent is withdrawn from the system,which helps to maintain heat balance quite easily for feedstock withhigh CCR (up to 20 wt %).

Catalyst Regenerator

The catalyst withdrawn from stripper is transported through standpipe tocatalyst regenerator. In the present invention, the superficial velocityin catalyst regenerator is maintained typically within 0.5–2.0 m/s andmore preferably within 0.8–2.0 m/s to have a conventional dense bedregeneration of the catalyst. However, the present invention is alsoapplicable to fast fluidized combustor or even two stage regeneratordesigns.

The air is maintained such that preferably total combustion is achievedand the coke on regenerated catalyst is preferably less than 0.1 wt %keeping the regenerator temperature within 730–750° C. Since the feedCCR and metals are preferentially deposited on the adsorbent particles,we do not expect too much coke lay down on the catalyst. However,catalyst cooler may also be employed in the present invention where theregenerator temperature is to be restricted within 730° C. for achievingdesired catalyst to oil ratio in riser.

Adsorbent Regenerator

The adsorbent regenerator usually runs in the partial combustion modeunder controlled airflow in dense bed fluidization regime. The cokeburnt from the adsorbent is sufficient to maintain the dense bedtemperature within 700° C. and most preferably within 680° C. The excessoxygen in the flue gas could be in the range of 0–2-vol % and CO/CO₂ mayvary in the range of 0.2–20 vol/vol. There is no maximum limit on thecoke on the adsorbent. Usually, it is observed that at higherconcentration of coke on the adsorbent, the vanadium and CCR trappingability of the adsorbent improves. However, for practical reasons, thecoke content on the adsorbent is kept in the range of 0.3–2.0-wt %.

There is provision to withdraw a net stream of adsorbent from theregenerator when the residue contains feed CCR above 8-wt % and thepreferred adsorbent in such case is calcined coke. This helps to processhigher CCR feed without violating the heat balance. The flue gas of theadsorbent regenerator is either mixed with the flue gas of catalystregenerator or sent directly to CO boiler or energy recovery section.

Riser

In this section, the adsorbent particles coming from adsorbentregenerator are first contacted with preheated heavy residualhydrocarbon feed in presence of lift steam. Typically, lift and feedatomization steam of about 10–50 wt % of feed may be added in the bottomsection of the riser depending on the quality of residue particularlyCCR content. The superficial velocity is maintained in the range of 6–10m/s typically, which will be sufficient to lift the adsorbent particlesthrough the riser.

The regenerated catalyst is injected at the intermediate elevation ofthe riser. The ratio of catalyst to total hydrocarbon is kept normallyin the range of 4–6 wt/wt to achieve best possible results. There isprovision for injecting separate feed stream at the intermediate riserelevation above the entry point of the regenerated catalyst. Such feedshould contain CCR, metals and other poisons as less as possible butdefinitely lower than those of the residual stream injected at the riserbottom. Typical example of such cleaner streams are fresh vacuum gasoil, heavy cycle oil etc. The riser top temperature and the intermediatetemperature just below the catalyst entry point is used to controlcatalyst/oil and adsorbent/residue ratios respectively through thecorresponding slide valve. Total residence time in the riser bottomsection (adsorbent entry point to catalyst entry point) could be 10–40%of the total riser residence time. The catalyst residence time in theriser is maintained between 1–15 seconds and preferably between 3–8seconds depending on the severity of the operation desired.

Stripper Cum Separator

The spent catalyst and coked adsorbent mixture enters the stripper cumseparator at a location near the interface of the catalyst/adsorbentlayer. In the present invention, stripper acts as a separator tosegregate catalyst from adsorbent and also has conventional FCC stripperto strip off all interstitial hydrocarbons from catalyst/adsorbent. Theprinciple of difference in minimum fluidization velocity betweencatalyst and adsorbent is exploited for achieving the segregation instripper.

Stripping steam may be injected at the bottom of the stripper cumseparator and/or at different elevations to achieve better strippingefficiency. Usually, 1.5–5 tons per 1000 tons of solid flow is thenormal ratio of total steam flow in the stripper. In the presentinvention, the superficial velocity of stripping gas is maintained inthe range of 0.1–0.4 m/s. However, it is preferred to maintain highervelocity of the stripping gas typically above 0.15 m/s, which is closeto the minimum fluidization velocity of denser particles for ensuringbetter segregation & stripping. Specially, in the standpipes and at thebottom of the stripper, steam purge is given to keep the adsorbent andthe catalyst mixture in fluidized state. In contrast to the conventionalstrippers, stripper without baffles/internals is preferred in thepresent invention considering practical issues such as generation ofdesired gravity head particularly for pushing catalyst/adsorbent towardsregenerator, better segregation efficiency, overall pressure balanceetc. However, stripper with baffles/internals is well within the scopeof the present invention.

BRIEF DESCRIPTION OF THE ACCOMPANIED DRAWINGS

FIG. 1 of the prior art represents prior art FCC apparatus with twostage regenerators, riser reactor with single stage annular stripper andwhere the entry of solid particles is at a single point in the riser.

FIG. 1 of the prior art represents a prior art with two separate densebed regenerator vessels.

Regenerator 1 of FIG. 1 receives spent catalyst from stripper 4.Combustion air 5 in the regenerator 1 is distributed at the bottom andcatalyst dense phase 6 is maintained typically in partial combustionconditions at which the coke on the catalyst is partially burnt offusing controlled amount of air at moderate temperature. The flue gas ofregenerator 1 is separated from the entrained catalyst by cyclone 7 or aseries of cyclones. The partially regenerated catalyst is lifted fromregenerator 1 to regenerator 2 via lift line 9 by using lift air 8 andplug valve 10. Secondary air 11 is introduced at the bottom ofregenerator 2 such that the dense bed 12 is maintained and the catalystis completely burnt off the coke to the extent of 0.1 wt %. The flue gasfrom regenerator 2 is separated from the entrained catalyst using seriesof cyclones 14 & 15 and discharged through outlet 16. The regeneratedcatalyst is withdrawn from line 13A having pressure equalizer 13B andfed to an entry 18 at the bottom of riser 3. Lift steam is introducedfrom inlet 17 of the riser 3 for pre-accelerating the catalyst.Hydrocarbon feed is injected at an entry 19 and the mixture ofhydrocarbon and catalyst flow through the riser 3 where the crackingreaction take place, the majority of hydrocarbon vapors are separatedfrom the said mixture in riser termination devices 20A & 20B. Theinterstitial hydrocarbons present in catalyst are stripped off instripper 4 with steam entering at 21. The stripped spent catalyst issent to the regenerator 1 through the standpipe 25 for continuousregeneration and circulation. The product hydrocarbons are furtherseparated from the entrained catalyst fines using cyclones 22A & 22B inreactor 23 before directing the product vapors to the fractionator viatransfer line 24.

FIG. 2 illustrates the FCC apparatus of the present invention where instripper cum separator 37 is employed to perform dual function firstlyas conventional stripper and secondly as separator device to separatecatalyst from adsorbent using steam 36 as a stripping/fluidizing media.The superficial velocity of steam in stripper cum separator 37 ismaintained in such a way that two distinctly different layers i.e. alayer of catalyst 62 and another layer of adsorbent 63 are formed instripper cum separator 37. The adsorbent layer 63 of stripper bed istaken to adsorbent regenerator 54 via coked adsorbent standpipe 52 andadsorbent flow is controlled through slide valve 53. Coked adsorbent isregenerated introducing oxygen containing gas or air or steam 59.Superficial velocity of gas is maintained in adsorbent regenerator 54 insuch a way that turbulent regime of operation is possible. Entrainedadsorbent particles are separated from flue gas via cyclones 55 & 56.Flue gas is taken out for further treatment through flue gas line 57where as adsorbent particles separated are dropped to adsorbent bed viacyclones 55 & 56 diplegs. An adsorbent cooler 58 is provided withadsorbent regenerator 54 for extracting excess heat produced. This willhelp in minimizing damaging effects of vanadium in high temperature andsteam environment. Reactivated adsorbent is transported to riser bottomentry 32 through reactivated adsorbent standpipe 60. Flow of thisadsorbent is controlled through slide valve 61. Reactivated adsorbent islifted up in the riser 35 using lift steam 31 entering right at thebottom of the riser 35. Steam 31 will facilitate to achieve fullydeveloped flow of reactivated adsorbent before it comes in contact withheavy residue feed entering at a location 33 above adsorbent entry point32. As soon as heavy residue feed 33 comes in contact with reactivatedadsorbent, feed gets vaporized and subsequently feed contaminants suchas Nickel, Vanadium, and Conradson carbon content (CCR) etc. aredeposited on adsorbent while feed and adsorbent are transported upwardsin the riser 35. Similarly, catalyst layer 62 of stripper bed istransported to catalyst regenerator 44 via spent catalyst standpipe 42and the catalyst flow is controlled through slide valve 43. Spentcatalyst is regenerated in catalyst regenerator 44 by introducing oxygencontaining gas or air through the inlet 49, which also causes catalystfluidization and proper mixing. Entrained catalyst is separated incyclones 45 and 46 provided in the dilute bed of regenerator 44.Catalyst is retained in regenerator and flue gas is taken out throughflue gas line 47. A catalyst cooler 48 is provided to cool down thetemperature of catalyst, if required. Catalyst cooler 48 is aconventional one adopted in FCC units. Regenerated catalyst is sent toan intermediate entry 34 of riser 35 through regenerated catalyststandpipe 50 by controlling catalyst flow through slide valve 51. By thetime mixture of feed and adsorbent comes in contact with regeneratedcatalyst entering at a location 34 in riser 35, feed is almost free fromall the contaminants. From entry point 34 in the riser 35 onwards,cracking reaction takes place and the feed, catalyst and adsorbentmixture is pneumatically conveyed to the riser top. Product andunconverted hydrocarbon vapors are separated from spent catalyst andcoked adsorbent through the riser termination devices 39A & 39B providedat the top end of the riser 35. Spent catalyst-coked adsorbent mixtureis brought to the stripper via dip leg of termination devices 39A & 39B.Fine particles of spent catalyst and coked adsorbent carried along withhydrocarbon vapors to the reactor 38 are separated using cyclones 40A &40B. The diplegs of 39A, 39B, 40A & 40B are terminated close to spentcatalyst and coked adsorbent bed interface in stripper cum separator 37.As described above, spent catalyst and coked adsorbent mixture collectedin stripper cum separator 37 is separated in to two layers 62 & 63 andtaken to respective regenerators 44, & 54 for regeneration/reactivation.The cycle of regeneration, feed contaminants removal, cracking reactionfollowed by gas-catalyst-adsorbent separation and then separation ofspent catalyst from coked adsorbent is continued. Though it is not shownin FIG. 2, riser 35 employed in the present invention may also belocated externally. In such situation, the cyclones are connected to theriser 35 top and the diplegs of these cyclones are connected to strippercum separator 37 at the interface of catalyst-adsorbent bed.

The present invention also includes recycling of coked adsorbent 63separated in stripper cum separator 37 directly to riser entry 32without under going regeneration step via recycle adsorbent stand pipe60(A) and slide valve 61 is used to control coked adsorbent flow toriser entry 32. Other wise, instead of oxygen containing gas or air,steam is used in adsorbent regenerator 54 for the purpose of keepingfluidization conditions required. This provision is very helpful whencalcined petroleum coke is used as an adsorbent. Though not indicated inFIG. 2 there is a provision for adding or withdrawing adsorbent andcatalyst to/from catalyst regenerator 44 and adsorbent regenerator 54.

FIG. 3 illustrates the FCC apparatus of the present invention whereinstripper cum separator (7) is employed to perform dual functions,firstly as a conventional stripper and secondly as a separator device toseparate catalyst from adsorbent using steam (6) as astripping/fluidizing media. The superficial velocity of steam instripper cum separator (7) is maintained in such a way that twodistinctly different layers (depending upon the particle size/density ofcatalyst and adsorbent) i.e. a layer of catalyst and another layer ofadsorbent (33 and 32) are formed in stripper cum separator (7).

The said catalyst/adsorbent layers (33 and 32) of stripper bed are takento catalyst/adsorbent regenerators (14 and 24) via stand pipes (12 and22) respectively and the flow of catalyst/adsorbent is controlled byslide valves (13 and 23) respectively. Coked adsorbent/spent catalyst isregenerated in regenerators (24 and 14) by introducing oxygen-containinggas or air or steam through inlets (29 and 19) respectively. Superficialvelocity of gas is maintained in said adsorbent/catalyst regenerator insuch a way that turbulent regime of operation is possible. Entrainedcatalyst/adsorbent particles are separated by cyclones (15, 16 and 25,26) respectively provided in the dilute bed of regenerators (14 and 24).Catalyst is retained in regenerator and flue gas is taken out throughrespective flue gas lines (17 and 27). Catalyst coolers (18 and 28) areprovided to cool down the temperature generated in the regenerators, ifrequired. Catalyst coolers (18 and 28) are conventional ones that areprovided to adsorbent and catalyst regenerators (24 and 14) respectivelyfor extracting excess heat produced. This will help in minimizingdamaging effects of vanadium in high temperature and increasing thecatalyst or adsorbent circulation rate. Flue gas is taken out forfurther treatment through flue gas lines (17 and 27) respectively.

Regenerated catalyst is transported to the riser entry (4) via standpipe (20) that is in flow communication with the regenerator (14).

Reactivated adsorbent is transported to the riser entry (2) via standpipe (30) that is in flow communication with adsorbent regenerator (24).

Regenerated catalyst flow is controlled by slide valve (21).

Reactivated adsorbent flow is controlled by slide valve (31).

Adsorbent is also transported directly into the riser (5) withoutreactivation via standpipe (30A).

Reactivated adsorbent is lifted up in the riser (5) using lift steam (1)entering right at the bottom of the riser (5). Steam (1) will facilitateto achieve a fully developed flow of adsorbent before it comes intocontact with heavy residue feed (3) entering at location of the riserabove the adsorbent entry point (2).

As soon as heavy residue feed (3) comes in contact with the reactivatedadsorbent, feed gets vaporized and subsequently feed contaminants suchas Nickel, Vanadium and Conradson carbon content (CCR) etc. aredeposited on adsorbent while feed and adsorbent are transported upwardsin the riser (5) pneumatically.

Regenerated catalyst is transported to the riser entry (4) via standpipe (20) that is in flow communication with catalyst regenerator (14).From entry point (4) in the riser (5) onwards, cracking reaction takesplace in presence of catalyst and the feed, catalyst and adsorbentmixture is pneumatically conveyed to the riser top. Product andunconverted hydrocarbon vapors are separated from spent catalyst andcoked adsorbent through the riser termination devices (9A and 9B)provided at the top end (5A) of the riser (5). Spent catalyst and cokedadsorbent mixture is brought to the stripper via dip leg of terminationdevices (9A and 9B) respectively. Finer particles of spent catalyst andcoked adsorbent carried along with hydrocarbon vapors to the reactor (8)are separated using cyclones (10A and 10B) respectively. The diplegs ofcyclones (9A, 9B, 10A and 10B) are terminated close to spent catalystand coked adsorbent bed interface in stripper cum separator (7). Asdescribed above, spent catalyst and coked adsorbent mixture collected instripper cum separator (7) is separated into two layers that is theupper layer of adsorbent (32) and lower layer of catalyst (33) and aretaken to respective regenerators (24 and 14) forreactivation/regeneration respectively. The cycle ofregeneration/reactivation, feed contaminants removal, cracking reactionfollowed by gas-catalyst-adsorbent separation and then separation ofspent catalyst from coked adsorbent and transportation of cokedadsorbent and spent catalyst to the respective regenerators iscontinued. Though it is not shown in FIG. 3, riser (5) employed in thepresent invention may also be located externally. In such situation, thecyclones are connected to the top end (5A) of the riser (5) and thediplegs of these cyclones are connected to stripper cum separator (7) atthe interface of catalyst and adsorbent bed.

Although not shown in accompanying drawings (FIG. 2 & FIG. 3), acombination of apparatus shown in FIG. 2 and FIG. 3 is also within thescope of present invention, wherein the outlets of the stripper cumseparator that are in flow communication with catalyst and adsorbentregenerators can be suitably modified depending upon the physicalproperties (size & density) of catalyst & adsorbent.

The present invention is further illustrated in the form of followingexamples in non-limiting way to better understand the invention.

EXAMPLE 1

This example illustrates the relationship between superficial gasvelocity and segregation efficiency in the said apparatus. Two types ofparticles i.e. sand of particle size in the range of 210–350 micronswith particle density of 2.6 g/cc and catalyst of size in the range of40–150 microns with particle density of 1.45 g/cc are used in thisstudy.

The apparatus is a circulating fluidized bed system consisting of ariser of diameter 6″ and of length 280″, having two stage cyclone systemfor gas-solid separation and a separator vessel of diameter 20″ ID andlength of 100″ with a provision for introduction of gas throughdistributor from its base and an entry for receiving catalyst-sandmixture, an outlet for taking out the catalyst via upper stand pipehaving flow communication with intermediate location in the riser,containing another outlet for sand withdrawal at the bottom of separatorvessel and having connected to riser via lower stand pipe.

The sequence of operation is continued till a steady state is reachedand then solid samples are collected at different locations along thelength of the separator. These samples are analyzed for particle sizedistribution to establish the amount of segregation that has takenplace. For 100% segregation efficiency, the collected samples shouldcontain no particles of size below 210 microns i.e. the minimum cut sizeof the sand employed in this study. Following results are obtained forthe gas superficial velocity in the range of 0.1 to 0.4 m/s with a totalinventory of 260 kg in the ratio of 50:50 (catalyst and sand).

Sup. Gas Segregation Velocity, m/s Efficiency, % Observation ≦0.03 — Nofluidization of sand particles 0.05 100 Rare movement of sand, twodifferent layers of catalyst and sand seen. 0.07 100 Slight movement ofsand and catalyst but still two layers are formed 0.12 100 Continuousmovement of sand and catalyst but still two layers are formed 0.15 100Rigorous movement of sand and catalyst and two distinctly differentlayers are formed 0.22 65–70 Considerable bubbling and mixing >0.30  50Rigorous bubbling and mixing

There was no fluidization and segregation of particles when thesuperficial velocity of gas was less than 0.03 m/s. 100% segregation isachieved with superficial gas velocity ranging from 0.05 to 0.20 m/s.However, superficial velocity beyond 0.3 m/sec leads to rigorousbubbling and mixing. It is apparent from the above study that there isan optimum superficial velocity of gas at which 100% segregation ispossible and also fluidization condition is maintained. It isinteresting to see that all conventional FCC strippers operate withsuperficial velocity of gas in the range of 0.1 to 0.3 m/s. In thepresent invention, stripper performs its function to remove strippablehydrocarbons and also facilitate segregation of solids within the samedomain of operation. Reduction in segregation efficiency beyond 0.3 m/sis due to rigorous bubbling and mixing of catalyst and sand particles.

From the above study, it is observed that rising bubbles are the drivingforce for particle segregation, facilitating movement of larger anddenser sand particles preferentially towards bottom of the separatorthrough the temporarily disturbed region i.e. voids created behind thebubbles. Similarly the up flow in the bubble wake (roof of the bubble)is causing smaller and lighter particles to reach top portion of thebed.

Normally particle segregation occurs if the superficial velocity of thegas in the vessel is maintained close to the minimum fluidizationvelocity of the larger and denser particle present in the vessel. It isinteresting to see in the table given below that the minimumfluidization velocity of the sand particles in the size range of 210–350microns employed in the present study is in the range of 0.06–0.12 m/s.Incidentally, 100% segregation efficiency is achieved corresponding tosuperficial gas velocity in the range of 0.05 to 0.15 m/s, which is onaverage, equivalent to minimum fluidization velocity of sand particles.Hence, in the present invention, the differences in minimum fluidizationvelocities between sand and catalyst particles are exploited to maximizethe segregation efficiency.

Material → Sand Catalyst APS, microns 180 280 325 425 95 Min. FluidVelocity, m/s 0.04 0.06 0.10 0.15 0.004

To sum up, the conditions prevailing in conventional FCC strippers wouldcause stripping as well as particle segregation within the operatingwindow. This example also highlights that driving force caused by risingbubbles leads to sand and catalyst segregation.

EXAMPLE 2

This example illustrates the benefits of sequential dual solidprocessing particularly the vanadium deposition preferentially on theadsorbent particles and thereby improving the activity of the FCCcatalyst.

For this purpose following samples are considered.

Catalyst-A Commercially available ReUSY (rare earth exchanged ultrastable Y) based FCC catalyst sample.

Adsorbent-B V-trap commercial additive with particle size in the rangeof 250–350 micron.

Vanadium is first deposited (by adopting pore volume impregnation routeof Mitchell) at 0 and 10,000 ppm on the mixture of catalyst A andadsorbent B, mixed in the ratio of 10:0.6.

Typically, the MAT activity was determined using MAT (micro activitytest) at 510° C. reactor temperature, 2.5 grams solid loading, 30seconds feed injection time and varying feed rate to generate data atdifferent conversion levels. Feed used is the combined feed used in onecommercial FCC unit with CCR 0.4 wt %, boiling range 370–550° C.,density of 0.91 g/cc.

There after, the Vanadium is deposited selectively on the adsorbent B at0,10000 ppm using the same pore volume impregnation technique. The metalladen adsorbent is then mixed with the catalyst A in the same ratio of0.6:10. MAT activity and product selectivity were measured using thesame feed with this solid mixture as performed in above.

For the sake of comparison, MAT studies were also done with onlyCatalyst A (without adding any adsorbent), both at 0 and 10000 ppmvanadium level.

Following results are obtained:

Mat Activity

Mat activity is defined as the conversion obtained at WHSV of 110 hour⁻¹and conversion is defined as the wt % product boiling below 216° C.including coke.

Vanadium Vanadium deposited on level, Composite Catalyst & Vanadiumdeposited ppm Catalyst A Adsorbent only on Adsorbent    0 38.6 — —10,000 10.1 16.5 37.5Coke Selectivity

Similarly, the coke selectivity changes with vanadium are given below,with both combined as well as sequential processing of solid. Here, cokeselectivity is defined as the coke yield (wt % of feed) at 38 wt %conversion level.

Vanadium Vanadium deposited on level, Composite Catalyst & Vanadiumdeposited ppm Catalyst A Adsorbent only on Adsorbent    0 1.87 — —10,000 5.93 3.62 1.9

It is observed here that if no adsorbent is used, vanadium at 10,000 ppmconcentration, brings down the conversion very significantly from 38.6to 10.1 unit, which improves to 16.5 when the adsorbent is used combinedin the catalyst. However, when sequential vanadium deposition is donefirst on the adsorbent before mixing with the catalyst, the solidmixture shows almost the same conversion as if no vanadium is there.Similar case is observed on the coke selectivity also. Sequentialvanadium deposition on the adsorbent first is able to provide cokeselectivity almost same as that of the catalyst without vanadium.

From the above, the importance and advantage of first depositingvanadium selectively on the adsorbent is clearly observed. There hasbeen remarkable retention of the catalyst activity, coke and otherproduct selectivity if the Vanadium is preferentially deposited on theadsorbent first before getting in contact with the actual catalyst.

Advantages

The following are the main advantages of the present invention.

-   1. The separation of spent catalyst and coked adsorbent is done at    low temperature in absence of any oxygen containing gas. At this    condition, there is no chance of vanadium mobility from the    adsorbent to the catalyst phase thereby eliminating catalyst    deactivation due to metal poisoning.-   2. The adsorbent contacts first with the residue hydrocarbons at the    riser bottom before contacting the cracking catalyst and captures    most of the feed contaminants such as Nickel, vanadium and CCR    present in the residue and thereby improving the activity and life    of catalyst. This greatly improves the capability of handling very    heavy residue feed economically and effectively. These results in    enhancing the overall performance of the catalyst and also to bring    down catalyst make up rate.-   3. The CCR and metal laden adsorbent can be withdrawn as separate    stream from the stripper cum separator or from adsorbent    regenerator. Such adsorbent may contain metals as high as 50,000    PPM, which could be used for extracting the high value vanadium and    nickel from the adsorbent.-   4. In addition, if the residue feed contains very high CCR (above 8    wt %), any state of the art FCC process, will require enormous    catalyst cooling to avoid the higher regenerator temperature. In    contrast, our invention takes care of very high CCR containing    residue quite efficiently. The adsorbent captures most of the feed    CCR (about 90%) in the riser bottom. In such cases of high feed CCR,    the preferred adsorbent is calcined petroleum coke. Such withdrawn    coke stream could be used as feed for coke gasification/power or    steam generation inside or outside the refinery. This unique feature    of our invention allows the flexibility to process residue with very    high CCR (as high as 20 wt % of feed) without violating the overall    heat balance of the unit.

1. A fluidized bed catalytic cracking apparatus, said apparatuscomprising: a riser (35) containing a feed stock, regenerated catalystand adsorbent and having a first inlet means (31) for introduction ofhigh velocity steam, a second inlet means (61) for introduction of thereactivated adsorbent, a third inlet means (32) for introduction of thefeed stock containing heavy residual fractions with high concentrationsof conradson carbon content, metals including vanadium and nickel andadditional poisons including nitrogen, a fourth inlet means (34) forintroduction of the regenerated catalyst, an outlet (35A) of the riseris connected to riser termination devices/cyclones (39A, 39B, 40A and40B) for causing separation of hydrocarbon vapors fromadsorbent-catalyst mixture, the cyclones having dip legs extendedtowards stripper cum separator (37) drops catalyst-adsorbent mixtureclose to the interface of catalyst and adsorbent bed; a reactor (38)comprising said cyclones and having an outlet (41) for taking outhydrocarbon vapors and steam mixture to fractionator(s); a stripper cumseparator (37) located at the bottom of the reactor for causing removalof strippable hydrocarbons from spent catalyst and coked adsorbentmixture and segregating catalyst from adsorbent; said stripper cumseparator is with or without baffles/internals having an inlet (36) atits base for introduction of steam in the upward direction so as toprovide a superficial velocity sufficient to strip off all hydrocarbonsand to segregate solids into two layers a, layer of spent catalyst (62)and another layer of coked adsorbent (63), an outlet at the bottom ofthe stripper cum separator for taking out coked adsorbent through astandpipe (52) via valve means (53), another outlet at an intermediatelocation above the said adsorbent outlet (52) for removing spentcatalyst through a standpipe (42) via a valve means (43); an adsorbentregenerator (54) located below the level of the lower portion of thestripper cum separator for receiving the coked adsorbent from the bottomportion of the stripper cum separator and causing reactivation ofadsorbent thereof; an inlet (59) in the adsorbent regenerator forintroduction of air or oxygen containing gas or steam, an outlet (60) inflow communication with the second inlet (32) of the riser forintroduction of reactivated adsorbent; and another outlet (57) at itstop for the disposal of flue gas; a catalyst regenerator (44) situatedabove the adsorbent regenerator but below the stripper cum separator isconnected to the stripper cum separator by the stand pipe (42), an inlet(49) at the base of the regenerator for introducing air or oxygencontaining gas for effectively burning coke deposited on the catalyst,an outlet (50) in flow communication with the fourth inlet of riser (34)via valve means (51) for introduction of regenerated catalyst; andanother outlet (47) at its top for disposal of flue gas.
 2. Theapparatus according to claim 1, wherein the outlets at the bottom andintermediate location of the stripper cum separator can be linked to thecatalyst and the adsorbent regenerators respectively when the spentcatalyst having particle size bigger and denser than that of the cokedadsorbent.
 3. A fluidized bed catalytic cracking apparatus, saidapparatus comprising: a riser (5) containing a feed stock, regeneratedcatalyst and adsorbent and having a first inlet means (1) forintroduction of high velocity steam, a second inlet means (2) forintroduction of the reactivated adsorbent, a third inlet means (3) forintroduction of the feed stock containing heavy residual fractions withhigh concentrations of conradson carbon content, metals includingvanadium and nickel and additional poisons including nitrogen, a fourthinlet means (4) for introduction of the regenerated catalyst, an outlet(5A) of riser is connected to riser termination devices/cyclones (9A,9B, 10A, 10B) for causing separation of hydrocarbon vapors fromadsorbent-catalyst mixture, cyclones having dip legs extended towardsstripper cum separator (7) drops catalyst-adsorbent mixture close to theinterface of catalyst and adsorbent bed; a reactor (8) comprising saidcyclones and having an outlet means (11) for taking out hydrocarbonvapors and steam mixture to fractionator(s); a stripper cum separator(7) located at the bottom of the reactor for causing removal ofstrippable hydrocarbons from spent catalyst, and coked adsorbent mixtureand segregating catalyst from adsorbent; said stripper cum separator iswith or without baffles/internals, an inlet means (6) at its base forintroduction of steam in the upward direction so as to provide asuperficial velocity sufficient to strip off all hydrocarbons and tosegregate solids into two layers a, layer of spent catalyst (33) andanother layer of coked adsorbent (32), an outlet means (12) at thebottom of the stripper cum separator for taking out spent catalystthrough standpipe via valve means (13), another outlet means (22) at anintermediate location for removing coked adsorbent through stand pipe(22) via valve means (23); an adsorbent regenerator (24) located belowthe level of the lower portion of the stripper cum separator forreceiving the coked adsorbent from the intermediate location of thestripper cum separator and causing reactivation of the adsorbentthereof; an inlet means (29) in the adsorbent regenerator forintroduction of air or oxygen containing gas or steam, an outlet means(30) in flow communication with the second inlet means (2) of the riserfor introduction of reactivated adsorbent via stand pipe (31), anotheroutlet means (27) at its top for disposal of flue gas; a catalystregenerator (14) situated above the adsorbent regenerator is connectedto stripper cum separator, an inlet (19) at the base of the regeneratorfor introducing air or oxygen containing gas for effectively burningcoke deposited on the catalyst, an outlet (20) in flow communicationwith the fourth inlet (4) of riser for introduction of regeneratedcatalyst via slide valve (21) and an outlet means (17) at its top fordisposal of flue gas.
 4. The apparatus according to claim 1, wherein theparticle size of the spent catalyst is smaller than that of cokedadsorbent.
 5. The apparatus according to claim 1, wherein the crackingcatalyst having a particle size in the range of 20–200 microns and aparticle density in the range of 1.0–1.8 g/cc.
 6. The apparatusaccording to claim 1, wherein the adsorbent having a particle size inthe range of 200–500 microns and a particle density in the range of1.5–3.0 g/cc.
 7. The apparatus according to claim 1, wherein thecatalyst regenerator having two stage cyclones means (55 and 66) forseparation of flue gas from adsorbent particles.
 8. The apparatusaccording to claim 1, wherein the adsorbent regenerator having adsorbentcooler means (58) for removal of excess heat from adsorbent regeneratorbed.
 9. The apparatus according to claim 1, wherein the catalystregenerator having two stage cyclones means (45 and 46) for separationof flue gas from catalyst particles.
 10. The apparatus according toclaim 1, where in a portion of the coked adsorbent is directly routed tothe riser from stripper cum separator outlet (52) via stand pipes (60A)without undergoing reactivation step.
 11. The apparatus according toclaim 3, wherein the particle size of the spent catalyst is bigger thanthat of the coked adsorbent.
 12. The apparatus according to claim 3,wherein the cracking catalyst having a particle size in the range of200–500 microns and a particle density in the range of 1.5–3.0 g/cc. 13.The apparatus according to claim 3, wherein the adsorbent having aparticle size in the range of 20–200 microns and a particle density inthe range of 1.0–1.8 g/cc.
 14. The apparatus according to claim 3, wherein a portion of the coked adsorbent is directly routed to the riser fromstripper cum separator outlet (22) via stand pipes (30A) withoutundergoing reactivation step.
 15. The apparatus according to claim 1,wherein stripping of entrained hydrocarbons from spent catalyst-cokedadsorbent mixture and segregation of spent catalyst from coked adsorbenttake place simultaneously in the stripper cum separator.
 16. Theapparatus according to claim 1, wherein the rising bubbles are thedriving forces for particle segregation in the stripper cum separator.17. The apparatus according to claim 1, wherein the superficial gasvelocity in stripper cum separator is in the range of 0.05–0.4 m/s,preferably in the range of 0.10–0.20 m/s for particle segregation. 18.The apparatus according to claim 1, wherein superficial velocity of thegas in the stripper cum separator varies within the range of ±20% ofminimum fluidization velocity of larger and denser particles forensuring fluidization and segregation.
 19. The apparatus according toclaim 1, wherein the superficial velocity in the adsorbent regeneratoris in the range of 0.5–2.0 m/s, preferably in the range of 0.8–1.5 m/s.20. The apparatus according to claim 1, wherein 100% segregation ofcatalyst from adsorbent is achieved even within the prevailing operatingconditions of conventional fluid catalytic cracking strippers.
 21. Theapparatus according to claim 1, wherein the difference in minimumfluidization velocity of smaller and lighter particles and those oflarger and denser particles is used to achieve the desired segregation.22. The apparatus according to claim 1, wherein coked adsorbent that isseparated from spent catalyst in stripper cum separator, is in reducingenvironment thereby eliminating adverse effects including thedestruction of Zeolite structure of vanadium on the catalyst.
 23. Theapparatus according to claim 1, wherein the riser extends throughstripper cum separator following the separation of hydrocarbon gas fromcatalyst-adsorbent mixture or an external riser.
 24. The apparatusaccording to claim 1, wherein the mass flow rate of the adsorbent to theriser is such that the heat carried by the adsorbent is sufficient tovaporize heavy hydrocarbon feed stock and mass flow of adsorbent is inthe range of 20–60 wt % of total solids circulation.
 25. The apparatusaccording to claim 1, wherein said adsorbent comprises micro spheresselected from a group consisting of calcined clay, calcined and crushedcoke, magnesium oxide, silicia-alumina and a bottom cracking additivefor selective removal of metals and feed CCR.
 26. The apparatusaccording to claim 1, wherein said catalyst comprises catalysts selectedfrom a group consisting of Rare earth exchanged Y zeolite, ultra stableY zeolite, non-crystalline acidic matrix and other zeolites selectedfrom ZSM-5.
 27. The apparatus according to claim 1, wherein partial andcontrolled burning is performed in said adsorbent regenerator to preventtemperature excursions beyond 690° C. to enhance the life of theadsorbent.
 28. The apparatus according to claim 1, wherein diplegs ofriser termination devices/reactor cyclones are located at the interfaceof spent catalyst and coked adsorbent mixture in stripper cum separator.29. The apparatus according to claim 1, wherein stripping of entrainedhydrocarbons from spent catalyst-coked adsorbent mixture and segregationof spent catalyst from coked adsorbent simultaneously take place instripper cum separator.
 30. The apparatus according to claim 1, whereinsaid stripper cum separator is with or without baffles/internals. 31.The apparatus according to claim 1, wherein the valve means provided onthe stand pipes are slide valves.